The present invention relates to a liquid pressure control valve adapted to be used with a liquid pressure type braking device. More particularly, the invention relates to a vehicle deceleration sensing type two-system liquid pressure control valve which senses the deceleration of a vehicle and automatically sets a crossover liquid pressure according to a variable load on the vehicle.
In order to suitably apply braking forces to the front and rear wheels of a vehicle, especially to those of an automobile, a liquid pressure control valve is provided in the liquid pressure circuit of the rear wheel brakes. In order to make the actual front and rear wheel braking force distribution ratio close to the ideal distribution ratio, it is desirable for the liquid pressure control valve to be able to vary the crossover liquid pressure according to the load on the vehicle, which, of course, is variable. Control valves of this type known in the art include a load response type control valve, which detects the relative displacement of the vehicle body and an axle or the like to change the crossover liquid pressure (or pressure-reducing-action start pressure), and a deceleration sensing type control valve which changes the crossover liquid pressure upon sensing a predetermined magnitude of deceleration.
On the other hand, FF (front engine, front wheel drive) vehicles, which have become popular recently, employ for safety purposes a so-called "diagonal split type brake system" The outlet of the master cylinder is divided into two systems, and one of the two systems is coupled to the right front wheel and the left rear wheel, while the other to the left front wheel and the right rear wheel. It is desirable for a control valve employed in this system to have a so-called "fault compensating function" in order to fully utilize the braking force in which, when one system is faulty, the pressure reducing action of the operable system is stopped so that the input liquid pressure is applied to the rear wheel brakes directly.
A deceleration sensing type liquid pressure control valve disclosed, for instance, by Japanese Published Patent Application No. 18421/1981 requires no link mechanism. Therefore, it is small in size, light in weight and low in manufacturing cost compared with a load response type liquid pressure control valve. However, in the case where a deceleration sensing type liquid pressure control valve is coupled to a two-system braking circuit, it is necessary to provide a deceleration sensing valve (inertial valve) and a piston for adjusting the compression of a control spring for each of the two liquid pressure systems. Therefore, in this case, it is rather difficult to reduce the size and weight of the valve body and to reduce its manufacturing cost.
For two-system liquid pressure control with this type of valve, the control pistons are depressed by respective springs. However, it is considerably difficult to make the loads of the two springs uniform, and therefore a liquid pressure difference occurs between the two systems, with the result that the braking forces are liable to be unbalanced.
Many other deceleration sensing type two-system liquid pressure control valves are known in the art. However, most of them are intricate in construction and accordingly high in manufacturing cost, and moreover have no compensating function.
In view of the foregoing, an object of the present invention is to provide a deceleration sensing type two-system liquid pressure control valve which is small in size, light in weight, low in manufacturing cost and high in performance.